1. Field of the Invention
The present invention relates to a method of producing an electrode and also to a method of producing a nonaqueous electrolyte battery.
2. Description of the Related Art
A remarkable attention is currently focused on nonaqueous electrolyte batteries having a high energy density as power sources for hybrid electric vehicles and as accumulators for generators using natural energy such as solar light and wind power. In these applications, changes in the amount of power generation and load as a function of time are abrupt and therefore, secondary batteries having high ability in fast charge and discharge of large current, that is, a large-current performance are required.
In order to cope with such a requirement, technical developments for improving the large-current performance of a nonaqueous electrolyte battery are being made. As one example of these techniques, a method using a positive or negative electrode active material having a smaller particle diameter, that is, a larger specific surface area is given. When the specific surface area of the active material is increased, the contact area between the active material and a nonaqueous electrolyte is increased. As a result, lithium ions can be transferred from the active material to the electrolyte with lower resistance, and therefore, battery voltage is not reduced when large current flows, thereby attaining a large-current performance.
Although the inventors of the present invention also have tried to improve the large-current performance of a battery by repeated contrivance to reduce the size of a particle of the active material, this, on the other hand, gives rise to new problems as the size of a particle decreases. In a process for producing an electrode of a nonaqueous electrolyte battery, first, an active material is suspended, together with a conductive agent and a binder, in a nonaqueous solvent to prepare a slurry. When this slurry was applied to a current collector used as a support through a die coater, the thickness of the coating was not fixed but became non-uniform. In an electrode in which the coating amount is non-uniform like this, current is concentrated on a part decreased in coating amount when flowing large current, with the result that only the part on which current is concentrated deteriorates quickly. As a result, this promotes deterioration of the capacity of the nonaqueous electrolyte battery and at the same time, increases electric resistance, causing a reduction in large-current performance.
JP-A 2004-321969 (KOKAI) relates to a coating apparatus in which a coating solution is continuously supplied from the central part of an extrusion type die coater. This invention intends to try to eliminate uneven thickness of a coating film and surface lines. JP-A 2004-321969 (KOKAI) is provided with at least one stirrer in a place where a coating solution is supplied to the die coater. And the aformentioned at least one stirrer is arranged between the part connecting a coating solution tank with a supply pipe and the distribution section of the die coater. Specifically, in the example, a stirrer is disposed at a position adjacent to the inside or outside of the supply port of the die coater. In this case, as the stirrer, a static mixer or a mesh filter is used.
Meanwhile, in the coating apparatus described in JP-A 2002-301417 (KOKAI), coating solutions stored in two supply tanks, that is, an A supply tank 18 and a B supply tank 19 respectively are mixed with each other and the obtained mixture solution is applied to a support 1 by using an extrusion die coater 4. The A supply tank 18 and the B supply tank 19 each have a feeder pump 10. A static mixer 20 is disposed between the extrusion die coater 4 and the feeder pump 10 to thereby mix the coating solution contained in the A supply tank 18 with the coating solution contained in the B supply tank 19 in the static mixer 20.